The present invention relates to a rolling-mill stand. More particularly this invention concerns a system for adjusting the relative axial positions of profiled rolls in such a stand.
When asymmetrical profiled steel goods, such as rails, sheet piling, guard rails, railroad plates, and the like are produced between a pair of rolls rotating about respective axes, these rolls are subjected not only to considerable radial forces, but to forces tending to displace them axially. Such axial forces can amount to 1000 kN to 2000 kN and can axially shift the rolls and produce a product whose profile is not what was intended.
In order to counter such axial shifting, it is standard to form the profiled rolls with axially oppositely directed annular abutment faces that extend nearly perpendicular, e.g. 87xc2x0, to the axis and that can be brought into axial contact with each other, thereby mechanically limiting any axial displacement. Such surfaces are subjected to considerable wear, even when heavily lubricated. Under the best of circumstances, these surfaces wear so that they must be machined down. This reduces their diameter and makes the abutment faces effective again.
It is also possible to simply brace the rolls via massive axial-thrust bearings against the roll-stand frame. Even so considerable elastic deformations of for example 1 mm to 4 mm per 100 kN are encountered due to the numerous elements effectively braced between the cast-iron roll-stand frame and the actual rollers.
This problem becomes somewhat more complex when the workpiece is reversed 180xc2x0 and sent back through the stand. In this case the axial forces can be additive and thus even more of a problem.
It is therefore an object of the present invention to provide an improved axial-positioning system for rolling-stand rolls.
Another object is the provision of such an improved axial-positioning system for rolling-stand rolls which overcomes the above-given disadvantages, that is which allows the rolls to be set in a position that will be maintained during the entire rolling operation and that takes into account all of the factors effecting axial roll position.
These are achieved, in accordance with the invention in a method of rolling a structural shape in a caliber mill or a method of adjusting the relative axial positions of a pair of rolls centered on respective parallel axes in a rolling-stand frame and having respective pairs of axially engageable abutment faces, the method comprising the steps of:
axially displacing one of the rolls in one direction into one end position with one of the pairs of faces pressing axially against other with a predetermined force and then in the opposite direction into an opposite end position with the other of the pairs of faces pressing axially against each other.
The structural shapes with which the invention is applicable include all structural shapes which, during the rolling between the rolling calibers can generate an axial force on the rolls in the direction of one or the other of the axially engageable or abutment faces or shoulders. These structural shapes include sheet piling, guard rails, railroad plates and certain rails, clamping plates mast steel for cranes and, in general, any structural shape including H-beams, I-beams, channels, modified I-beams and Z-shapes. Such structural shapes are also referred to as profiles in the industry.
According to the invention, the structural shape is rolled between the rolling calibers in the finishing operation to size the rolled structural shape. According to the invention, the rollers are axially positioned relatively by:
(a) shifting the one of the rolls axially in one axial direction to press the axially engageable faces on one side of said rolling calibers against each other and shifting that roll axially in an opposite axial direction to press the axially engageable faces on another side of the rolling calibers against each other with a defined force,
(b) storing values representing the positions of the one of the rolls upon axial engagement of the faces on each side of the rolling calibers with each other, a value of the axial stroke of the one of the rolls between engagements of the engageable faces on opposite sides of the rolling calibers, and a calculated mean position of the one of the rolls, and shifting the one of the rolls into a caliber-registering position of the rolls of the pair;
(c) then shifting the one of the rolls axially in one axial direction to press the axially engageable faces on one side of the rolling calibers against each other and shifting the one of the rolls axially in an opposite axial direction to press the axially engageable faces on another side of the rolling calibers against each other with incrementally increased forces, and storing respective values of the respective forces, respective values representing the positions of the one of the rolls upon axial engagement of the faces on each side of the rolling calibers with each other at the incrementally increased forces and values of the axial stroke of the one of the rolls between engagements of the engageable faces on opposite sides of the rolling calibers for the incrementally increased forces, and calculating from the stored values a relationship between spring constants of the frames with axial force on the rolls; and
(d) during rolling of the structural shape shifting the one of the rolls out of the caliber-registering position by an amount calculated from the spring response of the frames to an expected axial force to be developed during rolling into an actual rolling position, and maintaining the one of the rolls in the actual rolling position with a position controller.
A caliber roll mill according to the invention can comprise:
a mill stand having a pair of opposite mill-stand frames;
a caliber-roll pair including upper and lower caliber rolls journaled at opposite ends in respective ones of the mill-stand frames of a mill stand in respective bearing chocks, corresponding ends of the rolls being located at a service side of the mill stand and at a drive side of the mill stand at which the rolls are driven, the rolls having respective juxtaposed rolling calibers generating axial forces on the rolls upon rolling a structural shape between them and axially engageable faces flanking the rolling calibers, one of the rolls being axially shiftable relative to the other of the rolls, the one of the rolls having a roll stub at the service side;
a thrust bearing having inner rings on the stub and outer rings;
a piston receiving the outer rings;
a cylinder formed in a respective one of the bearing chocks receiving the piston and provided with means for pressurizing the piston on axially opposite sides thereof for displacing the one of the rolls axially in opposite directions; and
a displacement-measurement device mounted on the cylinder for measuring axial displacement of the piston.
The system used for controlling the axial positioning of the rolls can include a computer for:
(a) storing values representing the positions of the one of the rolls upon axial engagement of the faces on each side of the rolling calibers with each other, a value of the axial stroke of the one of the rolls between engagements of the engageable faces on opposite sides of the rolling calibers, and a calculated mean position of the one of the rolls, and shifting the one of the rolls into a caliber-registering position of the rolls of the pair;
(b) then shifting the one of the rolls axially in one axial direction to press the axially engageable faces on one side of the rolling calibers against each other and shifting the one of the rolls axially in an opposite axial direction to press the axially engageable faces on another side of the rolling calibers against each other with incrementally increased forces, and storing respective values of the respective forces, respective values representing the positions of the one of the rolls upon axial engagement of the faces on each side of the rolling calibers with each other at the incrementally increased forces and values of the axial stroke of the one of the rolls between engagements of the engageable faces on opposite sides of the rolling calibers for the incrementally increased forces, and calculating from the stored values a relationship between spring constants of the frames with axial force on the rolls; and
(c) during rolling of the structural shape shifting the one of the rolls out of the caliber-registering position by an amount calculated from the spring response of the frames to an expected axial force to be developed during rolling into an actual rolling position, and maintaining the one of the rolls in the actual rolling position.
The method and rolling mill of the invention has been found to reduce wear, minimize the usage and need for lubricant and has the further advantage of maintaining the caliber rolls practically continuously in such registry that high quality profiled products can be obtained, especially when, during the rolling of these products, there is a rotation of the stock between the reversing passes.